Using fuzzy controller for improvement of power decoupling performance in PV systems

ABSTRACT

In photovoltaic systems in order to ensure the stable operation of the module, ripple value of the input voltage should be mitigated to a small value; for this purpose, the power decoupling circuit can be used. In this work, considering the four-switch-based power decoupling circuit developed, the conventional Proportional-Integral (PI) controller has been replaced with well-known fuzzy controller, which enjoys a wide range of control gain variation, both linear and nonlinear rules' capability, robustness and more flexibility. The operating modes of the circuit are addressed and accordingly the space state model is derived. Then, the proposed controller has been replaced and the performance of the system will be analysed. The power decoupling circuit along with the proposed controller is implemented by MATLAB/Simulink software. The simulation results show the ability of the proposed fuzzy controller to improve the performance of the system in comparison to the conventional PI controller. A deeper comparison of two controllers confirms that the system would experience more accuracy, faster response and lower total harmonic distortion (THD) in presence of the proposed fuzzy controller.     

Quality of service‐aware approaches in fog computing

In recent years, fog computing, a novel paradigm, has emerged for location and latency‐sensitive applications. It is a powerful complement for cloud computing that enables provisioning services and resources outside the cloud near the end devices. In a fog system, the existence of several nonhomogenous devices, which are potentially mobile, led to quality of service (QoS) worries. QoS‐aware approaches are presented in various parts of the fog system, and several different QoS factors are taken into account. In spite of the importance of QoS in fog computing, no comprehensive study on QoS‐aware approaches exists in fog computing. Hence, this paper reviews the current research used to guarantee QoS in fog computing. This paper investigates the QoS‐ensuring techniques that fall into three categories: service/resource management, communication management, and application management (published between 2013 and October 2018). Regarding the selected approaches, this paper represents merits, demerits, tools, evaluation types, and QoS factors. Finally, on the basis of the reviewed studies, we suggest some open issues and challenges which are worth further studying and researching in QoS‐aware approaches in fog computing.     

Coreless Fiber‐Based Whispering‐Gallery‐Mode Assisted Lasing from Colloidal Quantum Well Solids

Whispering gallery mode (WGM) resonators are shown to hold great promise to achieve high‐performance lasing using colloidal semiconductor nanocrystals (NCs) in solution phase. However, the low packing density of such colloidal gain media in the solution phase results in increased lasing thresholds and poor lasing stability in these WGM lasers. To address these issues, here optical gain in colloidal quantum wells (CQWs) is proposed and shown in the form of high‐density close‐packed solid films constructed around a coreless fiber incorporating the resulting whispering gallery modes to induce gain and waveguiding modes of the fiber to funnel and collect light. In this work, a practical method is presented to produce the first CQW‐WGM laser using an optical fiber as the WGM cavity platform operating at low thresholds of ≈188 µJ cm^?2 and ≈1.39 mJ cm^?2 under one‐ and two‐photon absorption pumped, respectively, accompanied with a record low waveguide loss coefficient of ≈7 cm^?1 and a high net modal gain coefficient of ≈485 cm^?1. The spectral characteristics of the proposed CQW‐WGM resonator are supported with a numerical model of full electromagnetic solution. This unique CQW‐WGM cavity architecture offers new opportunities to achieve simple high‐performance optical resonators for colloidal lasers.     

Designing end-to-end resource reservations in predictable distributed embedded systems

Contemporary distributed embedded systems in many domains have become highly complex due to ever-increasing demand on advanced computer controlled functionality. The resource reservation techniques can be effective in lowering the software complexity, ensuring predictability and allowing flexibility during the development and execution of these systems. This paper proposes a novel end-to-end resource reservation model for distributed embedded systems. In order to support the development of predictable systems using the proposed model, the paper provides a method to design resource reservations and an end-to-end timing analysis. The reservation design can be subjected to different optimization criteria with respect to runtime footprint, overhead or performance. The paper also presents and evaluates a case study to show the usability of the proposed model, reservation design method and end-to-end timing analysis.     

On the stability and the stabilization of linear discrete repetitive processes

Multidimensional Systems and Signal Processing - This article deals with stability and stabilization issues for linear two-dimensional (2D) discrete models. More precisely, we focus on repetitive...     

Uniform synchronization in multi‐agent systems with switching topologies

This paper deals with uniform synchronization analysis of multi‐agent systems with switching topologies. The agents are assumed to have general, yet identical, linear dynamics. The underlying communication topology may switch arbitrarily within a finite set of admissible topologies. We establish conditions under which the network is uniformly synchronized meaning that synchronization is valid under all possible switching scenarios. The primary conditions established are in terms of a pair of Lyapunov strict inequalities. Following those conditions, small gain and passivity types of conditions are proposed under which uniform synchronization is guaranteed. The proposed results are also extended to the case of observer‐based protocols. Copyright © 2015 John Wiley & Sons, Ltd.     

Experimental and CFD analysis of photocatalytic gas phase vinyl chloride (VC) oxidation

Photocatalytic destruction of gas phase vinyl chloride (VC) was examined using experimental and computational fluid dynamics (CFD) approaches. Experimental work involved using a differential photoreactor for determining kinetics of oxidation and an annular flow photoreactor for overall removal investigations as well as comparison with CFD models. The kinetic data obtained from differential photoreactor were used to model and predict the performance of the annular photoreactor using CFD. The photocatalytic oxidation of VC followed first order kinetics for inlet concentrations up to about and CFD was able to predict the removal of VC in the system. Both experimental and CFD modeling showed the removal of VC in the system increased with increasing the VC loading rate. CFD analysis of the photoreactor also provided insight into the detailed concentration gradient of VC within the reactor. The modeling results indicated significant radial VC concentration gradient and non-uniform flow distributions in the annular photoreactor. This non-uniform flow distribution, in turn, resulted in short circuiting of the VC contaminated gas and may have resulted in less than optimum removal efficiency for VC in the annular reactor over the entire range of inlet VC concentrations. Overall, the information provided by CFD modeling and simulation showed to be valuable for reactor design modification and for improving the reactor performance.     

Friction and wear characteristics of steel on rock under water and oil based lubricated sliding conditions

Abstract

In recent years, drilling extended reach wells have become more and more common in the petroleum industry to optimise the oil and gas production. Extended reach wells are defined as wells that have two times more horizontal step out than true vertical depth. High friction (frictional torque) and drag are two of the mechanical limiting factors while drilling longer horizontal wellbores. There are numerous methods and tools developed to lower the drillstring friction. Drilling non-circular wellbores is a new concept with potential to minimise the mechanical friction by reducing drillstring and sidewalls contact area. However, this will cause an increase of contact pressure owing to the reduced contact area between drillstring and the formation. This article presents results obtained from an experimental study pertaining to the friction behaviour using a pin on disc set-up with steel pin and granite disc in the presence of water and oil based lubricants. These tests have been designed to represent frictional contact conditions between a rotating steel drillstring and the wellbore wall at different contact pressures. Test results show that the friction coefficient decreases with an increase of contact pressure in wet condition for both water and oil based lubricants. It is also observed that the friction factor increased by adding sand and phyllite particles to the water based lubricant. Considering the wear scars, the friction coefficient shows reduction with increased contact pressure in all tests with and without particles for both water and oil based lubricants.     

A Century of Fractionated Radiotherapy: How Mathematical Oncology Can Break the Rules

Radiotherapy is involved in 50% of all cancer treatments and 40% of cancer cures. Most of these treatments are delivered in fractions of equal doses of radiation (Fractional Equivalent Dosing (FED)) in days to weeks. This treatment paradigm has remained unchanged in the past century and does not account for the development of radioresistance during treatment. Even if under-optimized, deviating from a century of successful therapy delivered in FED can be difficult. One way of exploring the infinite space of fraction size and scheduling to identify optimal fractionation schedules is through mathematical oncology simulations that allow for in silico evaluation. This review article explores the evidence that current fractionation promotes the development of radioresistance, summarizes mathematical solutions to account for radioresistance, both in the curative and non-curative setting, and reviews current clinical data investigating non-FED fractionated radiotherapy.